Wire stitching apparatus are employed in book binding machine for stapling bunch of paper sheets to form a note books etc. One such conventional wire stitching machine is shown in FIG. 1. According to FIG. 1, conventional stitching machine includes the stitching head (1) that reels out a wire from the wire spool (2) and then cuts the wire (W) in a predetermined length, bends the wire into a U-shaped and drives the U-shaped wire into the set of sheets. Simultaneously when the wire (W) is driven, both ends of the U-shaped wire passed through the set of sheets are bent to staples the set of sheets.
One such wire stitcher for binding sets of sheets has been disclosed in the U.S. Pat. No. 4,328,919 that comprises a stitcher head having wire advancing and cutting mechanism for pulling the length of wire from the spool and applying on the paper sheets to be stitched.
However, the above set up of stitching mechanism carry difficulties leading to improper stapling of the product. In this conventional stitching machine, the stitching wire is directly pulled by the stitching head from the spool that leads towards the improper feeding of wire from the spool. Hence, the problem of uneven length of stitching pin which deteriorates the quality of product is arisen. In such machines, the stitching head is permitted to freely pull the wire from the reel with the result that the reel has unrestrained rotation in the direction of the unreeling of the wire, and this has been found to be objectionable in that the unreeled wire is too loose and is apt to become tangled or kinked, with the result that the staples formed are uneven or are improperly applied to the paper sheets. Hence, when the wire spool is fully loaded with wire, then in such situation, stitching head require more load to pull the wire due to more weight. This result in small length of pins due to slippage and also affect the life span of the stitching head due to overload. Adversely, when the spool weight is reduced, excessive length of wire is pulled out that result into the more length of pin.